Technical Field
The present invention relates to a driving support apparatus which automatically controls speed of a vehicle.
Related Art
A technique is known for automatically controlling speed of a vehicle on a curve in a road. In JP-A-2008-290469, a speed control apparatus is disclosed which controls speed of a vehicle by using a value, which is obtained by multiplying a rate of change of a curvature of the road by a proportional gain, as target longitudinal acceleration (target forward and backward acceleration). Thus, the speed control apparatus decreases the speed of the vehicle when the curvature of the road calculated from location information obtained from a GPS signal tends to increase, while increasing speed of the vehicle when the curvature of the road tends to decrease.
In the speed control apparatus disclosed in JP-A-2008-290469, a value is used, which is obtained by multiplying a rate of change of a curvature of a road by a proportional gain, as a target longitudinal acceleration. Thus, when the rate of change of the curvature of the road is constant, the target longitudinal acceleration also becomes constant. Some roads have different curvatures, though the rates of change of the curvatures are the same. According to the speed control apparatus disclosed in JP-A-2008-290469, the same target longitudinal acceleration is used for roads having different curvatures, if the rates of change of the curvatures are the same.
When the same target longitudinal acceleration is used for roads having different curvatures, the vehicle may not turn along the curvature of the curve in the road. This is due to different cornering forces acting on the roads having different curvatures. Even when the vehicle travels at a constant target longitudinal acceleration, higher lateral acceleration is applied or a side skid may be caused depending on the magnitude of the curvature. Thus, traveling stability of the vehicle cannot be assured. In addition, when the traveling stability of the vehicle cannot be maintained, the vehicle cannot smoothly travel on the curve in the road.